Visual inspection systems can be designed for use by human inspectors or for "machine vision" systems. In recent years, with the miniaturization of electrical and electromechanical devices, a particular need has arisen for inspection systems capable of detecting flaws in objects having very small features.
Most inspection systems include some sort of light source. Conventional light sources include incandescent and fluorescent lamps and light emitting diodes. Various optical arrangements have been designed for better illumination, such as ringed lamp arrays, focussed filament projectors, and fiber optic emitters. However, these conventional illuminators tend to result in "hot spots" and other viewing difficulties.
U.S. Pat. No. 5,051,872, entitled "Hemispherical Non-Glare Illuminator", assigned to Texas Instruments Incorporated, describes an illuminator that provides shadowless and uniform illumination. The illuminator has a translucent hemispherical diffuser that is placed between a light source and the object to be viewed. The concavity of the diffuser is toward the object to be viewed. The diffuser absorbs light incident on the convex surface, and emits the light diffusely from the concave surface.